Method of using syntactic foam to reduce noise and machine using same

ABSTRACT

A method of decreasing engine noise in machines, such as internal combustion engines, by replacing metallic engine components that serve as noise transmission pathways such as oil pans, valve covers, gear covers with similar components made of syntactic foam with a density of at least 0.5 g/cm 3  and a hardness at least about equal to that of an equivalent metallic engine part which it is replacing. The syntactic foam is comprised of fluid-filled microballoons in a foam matrix. The microballoons have an outer shell harder than that of the surrounding foam matrix, and a majority of the microballoons are out of contact with one another.

RELATION TO OTHER PATENT APPLICATION

This application claims priority from provisional application No. 60/858,885, filed Nov. 14, 2006, with the same title.

TECHNICAL FIELD

The present disclosure relates generally to substituting equivalent syntactic foam for metal in engine component(s) to reduce noise, and more specifically to replacing metallic engine components such as oil pans or valve covers with comparable pieces made from syntactic foam in order to reduce noise.

BACKGROUND

Internal combustion engines necessarily involve moving parts and explosive combustion events, and these things necessarily involve noise output. Governmental regulations require that this noise output be below a certain level. This has led to complex structures and “add-ons” to engines to try to reduce the noise output from components that act as the prime transmission path of sound such as valve covers, engine blocks, front and rear gear covers, oil pans and other engine components known to those skilled in the art. These add-ons can have the drawback of being bulky and increasing total cost of production.

One solution to this problem that has been considered is metallic components with isolation seals, however these have the drawback in that they can increase total engine cost and can leak. Another possible solution is laminated metal components such as QuietSteel. Components using this material, however, are hard to form and become quite difficult to weld. A related solution was proposed in U.S. Pat. No. 5,566,721 which involved coating a component, such as a driveshaft tube, with a sound deadening material such as a urethane elastomer. This method adds an extra production step and cost in terms of both capital and time. Other solutions have included the use of polymeric composite components with low density such as balsa wood, pvc foam or honeycomb inserts, but these can suffer from the problem of low strength and be damaged easily, which would make them difficult to use effectively in engine components. A final solution has been to use gas-assisted injection molded composite components, but this technology requires very specific parameters in terms of the heat and pressure of the surrounding environment. Thus it becomes difficult to achieve a uniform density/size of voids in the foam, so thus far this technology is only used in manufacturing relatively small pieces such as car door handles.

This disclosure is directed toward one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, a machine comprises a plurality of machine components being attached to one another, where at least one of the components is comprised of syntactic foam. The syntactic foam includes a polymer matrix and a plurality of fluid-filled microballoons which have a density of 0.5 g/cm³ or greater and a hardness of at least about Shore D 74. A majority of the microballoons are out of contact with one another, and each microballoon is composed of a shell more rigid than the surrounding matrix, and contains a fluid comprising a majority of the volume of the microballoon.

In another aspect, an engine comprises a plurality of engine components which are attached to one another. A portion of the engine components are metallic components and the other portion of the engine components comprise syntactic foam.

In still another aspect, a method of reducing sound emitted from a machine is accomplished by substituting a syntactic foam machine component for a metallic machine component.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged cross section of the syntactic foam according to the present disclosure;

FIG. 2 is an enlarged cross section of another syntactic foam according to the present disclosure; and

FIG. 3 is a diagrammatic side view of engine components which could be constructed of syntactic foam according to the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 1, there is shown a syntactic foam 10 comprised of a plurality of microballoons 11 a, b in a foam matrix 14, where the majority of microballoons are out of contact with one another. One example of a production method for such a syntactic foam is shown in U.S. Pat. No. 4,788,230, which teaches a specific method for making a lightweight foam. In contrast, the focus of this disclosure is to make a foam with sound deadening properties. Each microballoon 11 a, b has an outer shell 13 a, b which is of greater hardness than the surrounding foam matrix 14. It will be understood that the microballoon shell 13 a, b may be roughly 10% of the total diameter of the microballoon 11 a, b so that the microballoons 11 a, b can withstand the pressure put on them during the manufacturing process, and other expected forces and stresses. Each microballoon 11 a, b encloses a volume 12 a, b, wherein the majority of said volume 12 a, b is filled with some fluid, such as any suitable gas. The microballoons may range from 1 micron to 1000 microns in diameter, as will be known to one skilled in the art. It will further be understood that though FIG. 1 shows microballoons of two different diameters 11 a, b the scope of this disclosure is intended to include syntactic foam containing solely one size of microballoons or any combination of microballoons of different sizes, dependant upon the specific heat, electric and sound reduction properties and other criteria required for the specific component to be manufactured as will be known by one skilled in the art. Finally, it will be understood that though FIG. 1 only shows the syntactic foam 10 and microballoons 11 a, b, there may or may not be any one of a number of filler materials or crosslink additives in accordance with the desired characteristics of the foam.

Referring to FIG. 2, another syntactic foam 110 magnified cross section has a formulation similar to that of the foam 10 of FIG. 1, but also includes fibers 118 for increased strength. The FIG. 2 embodiment also differs in that the relative ratio of microballoons to polymeric matrix is greater than that of the syntactic foam of FIG. 1.

One set of materials proposed as components of the syntactic foam 10 are bisphenol A epoxy as a matrix resin, aromatic amine as a crosslink additive, glass fluid-filled microballoons and carbon fiber as a fiber filler as necessary. A second example of the syntactic foam 10 includes bisphenol F epoxy as a matrix resin, aliphatic amine as a crosslink additive, ceramic fluid-filled microballoons and basalt fiber as a fiber filler as necessary.

Other options for the matrix resin include but are not limited to: epoxy phenolic, epoxy cresol, epoxy BPA, aromatic epoxy, acrylic resins, bismaleimides maleic acid, isophthalic acid, orthophthalic acid, terephthalic acid, furfuryl alcohol, dicyclopentadiene diamines, or aromatic cyanate ester, or any appropriate combination or accepted equivalent.

Some possible materials that could be used as crosslink additives include but are not limited to: novolac polyamine, novolac fumaric acid, novolac glycols, polyacrylate polyglycols, styrene, acrylic acid, methacrylic acid, 1-4 butanediol, MOCA or UV and EB cure systems, or any appropriate combination or accepted equivalent.

One skilled in the art will understand that syntactic foam 10 necessarily involves the use of microballoons 11 a, b, however other fillers may be used to change the specifications or properties of the foam as desired for the specific application. Possible materials that could be used as fillers include but are not limited to: expanded clay prills, glass fiber, perlite, wood flour/fiber, expanded fly ash, corn stover/husk/cob, fly ash cenospheres, rice hull, rice hull ash, expandable starch granules, cotton wool/linters, hair or feather fiber, expanded thermoset such as phenolic granules, hemp/jute/kenaf fiber, rock wool, graphite fiber, aramid fiber, nylon fiber, other cellulosic or crop fiber, thermoplastic fiber, thermoset fiber or other mineral fibers such as asbestos, or any appropriate combination or accepted equivalent.

It is finally envisioned that the syntactic foam 10 could also be composed of: phenolic (phenol mixed with formaldehyde), polyether polyols, polyester polyols, polyimide resins or high heat-distortion thermoplastic resins, or any appropriate combination or accepted equivalent.

One skilled in the art will understand that the above examples are merely listed as exemplary options and are in no way intended to specifically limit the scope of the materials used and equivalent substitutes as defined by the current art may be used as desired. Further, one skilled in the art will understand that some combinations of the materials above may involve less ingredients, such as thermoplastics which do not require a cross-linking additive. The specific combinations of the materials listed above will be recognized by one skilled in the art.

Referring to FIG. 3 with continued reference to FIGS. 1 and 2 there is shown an engine housing 22 including valve cover components 20 a-c as well as an oil pan 21, amongst various other components. It is envisioned that according to the present disclosure any number of components of the engine housing 22 including the valve cover components 20 a-c or the oil pan 21 could be composed of syntactic foam 10 as described above with a minimum hardness at least equal to that of an equivalent metallic component which it is replacing. The specific examples of FIGS. 1 and 2 have hardness ranges of about Shore D 74 to about Shore D 80, respectively. The term “about” means that when the number is rounded off to the same number of significant digits, the numbers are equal. For instance, 73.5 is about 74. Although syntactic foam components having these hardness parameters may be suitable for the identified engine compressions, higher and lower harnesses would be attainable without difficulty. However, parts made at lower durometers would likely not be as durable for engine component applications, but higher durometers might be attractive, and would certainly be attainable with a suitable polymer content. Further, one skilled in the art will recognize that the description of the valve cover or oil pan components is intended to be exemplary only and other parts or components of the engine or engine housing 22 can be constructed from syntactic foam 10 in order to reduce noise. The present disclosure might be especially applicable to covers and the like that protect other machine components and include fastener bores for receiving suitable fasteners, such as bolts or screws.

INDUSTRIAL APPLICABILITY

One skilled in the art will recognize that the foam matrix 14 itself will have inherent sound reduction properties, but these properties can be improved by adding fluid filled microballoons 11 a, b. These microballoons 11 a, b increase sound reduction in two ways. The first is that they increase the complexity of the sound path through the foam by adding internal reflection barriers into the path once the sound enters the fluid-filled microballoons. Additionally, each time the sound goes through a barrier into a different medium, such as air to foam matrix 14, foam matrix 14 to microballoon shell 13 a, b, and microballoon shell 13 a, b to microballoon internal fluid 12 a, b a portion of the sound is scattered. By increasing the barrier changes in the sound path the sound will be increasingly scattered throughout the foam, and the sound emerging from the foam ultimately reduced.

As described above, it is envisioned that any number of metallic engine parts may be replaced by syntactic foam 10 made of fluid filled microballoons 11 a, b in a foam matrix 14 in order to reduce noise from the engine. Methods of part forming are various. These could include compression molding, transfer molding and injection molding. Since the syntactic foam composite material is relatively incompressible, unlike most common foams, it may be processed in normal pressure forming equipment. It may be necessary to process the part like a similar solid composite material (based upon the polymer content of the formulation), which may allow early demolding, but also a relatively long open cure time.

One preferred low cost formulation of the foam involves a foam comprised of 57% epoxy resin, 9% epoxy crosslinking agent, 22% fibrous filler, 6% microballoons and 6% long-fiber filler. This composite foam is roughly 30% lower density than comparable foam involving glass-filled spheres, and has desirable acoustical and physical properties for the intended application. This foam has a specific gravity of roughly 1.04 g/cm³ and a Durometer hardness of 80D (Shore D 80).

Another formulation involves a foam comprised of 59% epoxy resin, 9% epoxy crosslinking agent, 23% fibrous filler, 6% microballoons and 3% long-fiber filler as described above. This compound is roughly 40% lower density than a comparable foam involving glass-filled spheres, and also has desirable acoustical and physical properties for the intended application. This foam has a specific gravity of roughly 0.88 g/cm³ and a Durometer hardness of 75D (Shore D 74).

Still another formulation for the foam involves a foam comprised of 65% epoxy resin, 10% epoxy crosslinking agent, 13% carbon fiber filler and 13% microballoons. This formulation may be higher cost, but is 40% lower density than a comparable foam and has excellent acoustical and physical properties. This formulation of the foam has a Durometer hardness of 75D (Shore D 75) and a specific gravity of 0.88 g/cm³.

Another formulation involves a syntactic foam comprised of 81% epoxy resin, 12% epoxy cross linking agent, 3% fibrous filler and 4% microballoons. This foam has a specific gravity of roughly 1.94 g/cm³ and a durometer hardness of about Shore 74 D.

It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present invention in any way. One skilled in the art will recognize that although this disclosure focuses on replacing metallic engine parts, especially non-structural components, with syntactic foam to reduce noise, the scope includes other machines with internal combustion engines such as lawn mowers, leaf blowers, on-highway trucks and tractors, amongst other examples which will be known to one skilled in the art. Thus, those skilled in the art will appreciate that other aspects of the invention can be obtained from a study of the drawings, the disclosure and the appended claims. 

1. A machine comprising: a plurality of machine components being attached to one another, and at least one of the components being comprised of syntactic foam; the syntactic foam including a polymer matrix and a plurality of fluid-filled microballoons, a density of 0.5 g/cm³ or greater, and a hardness of at least about Shore D 74; and a majority of the microballoons being out of contact with one another, and each microballoon including fluid surrounded by a shell more rigid than the matrix, and the fluid being a majority of a volume of each microballoon.
 2. The machine of claim 1 wherein the machine being an engine, and the at least one component includes a valve cover.
 3. The machine of claim 1 wherein the at least one component includes a gear cover.
 4. The machine of claim 1 wherein the at least one component includes an oil pan.
 5. An engine comprising: a plurality of engine components being attached to one another and including a portion being metallic components and a portion being comprised of a syntactic foam component.
 6. The engine of claim 5 wherein the syntactic foam component includes a valve cover.
 7. The engine of claim 5 wherein the syntactic foam component includes a gear cover.
 8. The engine of claim 5 wherein the syntactic foam component includes an oil pan.
 9. The engine of claim 5 wherein the syntactic foam includes a density of 0.5 g/cm³ or greater.
 10. The engine of claim 5 wherein the syntactic foam includes a hardness of at least about Shore D
 74. 11. The engine of claim 5 wherein the syntactic foam includes a polymer matrix and a plurality of fluid-filled microballoons, and a majority of the microballoons being out of contact with one another.
 12. The engine of claim 5 wherein the syntactic foam includes a polymer matrix and a plurality of fluid-filled microballoons, and each microballoon includes a fluid surrounded by a shell more rigid than the matrix and the fluid being a majority of a volume of each microballoon.
 13. The engine of claim 12 wherein the syntactic foam components include at least one of a valve cover, a gear cover, and an oil pan; and the syntactic foam includes a density of 0.5 g/cm³ or greater, a hardness of at least about Shore D 74, and a majority of the microballoons being out of contact with one another.
 14. A method of reducing sound emitted from a machine comprising a step of: substituting a syntactic foam machine component for a metallic machine component.
 15. The method of claim 14 wherein the machine being an engine, and the machine component including at least one of a valve cover, a gear cover, and an oil pan.
 16. The method of claim 14 wherein the syntactic foam component includes a polymer matrix and a plurality of fluid-filled microballoons, a density of 0.5 g/cm³ or greater, and a hardness of at least about Shore D 74; and a majority of the microballoons being out of contact with one another, and each microballoon including fluid surrounded by a shell more rigid than the matrix, and the fluid being a majority of a volume of each microballoon. 